The invention relates to an apparatus and a method for determining the oil content of wax samples. In particular it relates to an apparatus and method for rapidly conditioning a wax sample and the determination of its nuclear magnetic reasonance (NMR) value, which is correlated with the oil content of the wax sample.
The oil-in-wax determination is a very important analytical tool in the operation and control of a wax manufacturing unit. Traditionally, the oil content of wax samples has been determined by sending samples from the unit to a laboratory for analysis by ASTM Method D-721 (See Annual Book of ASTM Standards, Part 18, page 129, Nov., 1970). Moreover, effective operation of a commercial deoiling unit is largely dependent upon the determination of oil content in the raw wax stream.
Determination of the oil content of the ASTM method requires that the wax sample be dissolved in methyl ethyl ketone (MEK), then cooled to -32.degree. C to precipitate the wax, followed by filtering. The oil content of the filtrate is then determined by evaporating the MEK and weighing the residue. The accuracy of the determination is reported to be .+-. 0.1% w, but experience has shown that values obtained in routine testing can vary by more than twice that much.
The ASTM test requires a minimum of 1 man hour per test, but the delivery of a sample to the laboratory, scheduling, testing, and reporting of results back to the operating unit, generally results in a time lapse of about 4 hours. The limited reliability of the test frequently results in a reluctance of the unit operator to bypass good wax storage with apparently off-specification wax, or to go back to good wax storage with wax apparently passing specification, unless the analytical results are clear cut, without a second confirming analysis. Thus, a full 8-hour shift can pass before the final disposition of the product wax stream is made. This uncertainty can require reprocessing a large quantity of good wax product, or cause the contamination of a good wax storage tank by failure to divert the stream during plant upsets. Thus, there is considerable economic incentive for the development of a more rapid and reliable means of determining the oil content of product wax streams.
Recently, a relatively inexpensive, broad-line, nuclear magnetic resonance (NMR) instrument called a "Quantity Analyzer," which measures liquids in solids has become commercially available. The adaptation of this equipment to the rapid and reliable determination of the oil content of refinery wax streams is the object of the invention.